Closes gh-15639

Spring Boot provides two separate auto-configurations that can
potentially expose an `AsyncTaskExecutor` implementation so relying on
the presence of a single instance is too weak.

This commit fixes the detection of the AsyncTaskExecutor that can be
used to bootstrap JPA so that a single instance is used and, in the case
more than one exists, the one named `applicationTaskExecutor`.

Closes gh-15447

Closes gh-15447

Closes gh-15451

See gh-15451

Closes gh-15634

Closes gh-15618

Closes gh-15622

Closes gh-15621

Closes gh-15620

Closes gh-15619

Closes gh-15618

Closes gh-15617

Closes gh-15616

Closes gh-15615

Closes gh-15614

Closes gh-15613

Closes gh-15612

Closes gh-15611

* pr/15610:
  Fix the anchor for the Micrometer Elasticsearch section

Closes gh-15610

* pr/15603:
  Polish "Ensure checking customizer ordering"
  Ensure checking customizer ordering

Closes gh-15603

See gh-15603

* gh-15472:
  Polish "Order actuator security config after resource-server config"
  Order actuator security config after resource-server config

Closes gh-15472

See gh-15472

Fixes gh-15539